This invention relates to mechanical displacement measuring apparatus and more particularly, to linear variable displacement transducer applications. And furthermore, relates to a system and method for utilizing the measuring apparatus to control a locomotive.
The use of strain gauges having a variable resistance as a function of strain applied to a tested member has been utilized to narrowly ascertain the strain at specific points on the surface of a structural member under load. In a large hollow unit, for example, the strain sensors may be mounted externally or internally on the surface of the member, and further must be mounted in pairs to differentiate the bending moment errors introduced by actual deformation in other than linear fashion. As is known in the art, the strain gauges are usually located at the part of the structural member undergoing the greatest strain (i.e., the thinnest part, or the site most likely to undergo deformation).
For relatively long structural members having substantially constant cross-sections, the use of a number of strain gauges is required to first ascertain the collective strain over the entire member, and secondly to offset bending moment errors introduced by structural bending.
Alternatively, a pair of resistive strain gauges may be located on opposing points of a longitudinal structural member and by assessing the difference in strain gauge readings, the bending moments may be eliminated and further the remaining strain is extrapolated to a value sufficient to describe the total strain over the length of the member.
In the operation of a locomotive pulling a load through a draw bar and a locomotive coupler, it is often desirable to maximize the strain upon the draw bar and thereby maximizing the force and work delivered from the locomotive to its load. In the past, several indirect methods have been used to maximize the useful work output of a locomotive. One method has been to monitor the ground speed of the locomotive and concurrently monitor the speed of the locomotive wheels in an attempt to prevent excessive wheel slip. This method has several problems. First of all, it is an indirect measure of the actual work output of the locomotive, and as such it is limited in its ability to provide the ultimate desired results. Furthermore, the accuracy and the sensitivity of the measurements necessary for this method need improvement.